The present invention relates to a method for making vegetable oil-based polyols. Still further, the present invention includes using vegetable oil-based polyols to produce polyurethane resins for use as casting compounds for electrical applications.
Polyols may be produced from petroleum. However, vegetable oils come from renewable resources. Vegetable oil molecules must be chemically transformed in order to introduce hydroxyl groups. For instance, soybean oil does not contain any hydroxyl groups but has on an average about 4.6 double bonds per molecule. The unsaturated portions of the vegetable oil molecule can be converted to hydroxyl groups. However, many reactions for preparing polyols from vegetable oils are not very selective. By-products, in addition to alcohol groups, are created during the transformation. Furthermore, many conventional methods of preparing polyols from vegetable oil do not produce polyols having a significant content of hydroxyl groups. Still further, many available methods of preparing polyols from vegetable oils do not produce products having a desirable viscosity. Greases or waxes often result as a consequence of such chemical transformations.
Conventionally, cast electrical components such as dry voltage transformers and insulators are formed from epoxy resins. Epoxy resins are rather expensive to use. Still further, epoxy resins are not easy to handle at low temperatures and have poor elasticity. Polyurethane resins prepared with castor oil have also been produced. However, these resins tend to be rubbery and thus undesirable for certain casting applications. Still further, castor oil-based polyurethanes have some limitations due to their higher price and environmental problems related to their by-products.
In order to overcome the deficiencies found with conventional processes for making vegetable oil-based polyols, a method for making vegetable oil-based polyols from vegetable oil or epoxidized vegetable oil is needed for a variety of applications including preparation of, through polyurethane chemistry, a resin for use as an electroinsulating casting compound, which is another embodiment of the present invention. Still further, this method of making vegetable oil-based polyols should avoid substantial side-reactions, such as esterification, cyclization, polymerization, and other undesirable reactions, and should produce polyols having a high hydroxyl content and a desirable viscosity.